UISI: Alice does not encrypt for Bob

[kegsay]

Steps to reproduce

Given this test case, this can fail because:

[@user-2-bob:hs1] console.log    WARN matrix_sdk_crypto::machine: Failed to decrypt a room event: Can't find the room key to decrypt the event, withheld code: None
    at /home/runner/.cargo/git/checkouts/matrix-rust-sdk-1f4927f82a3d27bb/7440ce0/crates/matrix-sdk-crypto/src/machine.rs:1513
    in matrix_sdk_crypto::machine::decrypt_room_event with room_id="!srZZtCsrpUMQZviMzy:hs1" sender="@user-1-alice:hs1" event_id="$tjgtkiA8rDy1tHcXDxaBN9QwcukLqnmmIxUZBrZEHhc" algorithm="m.megolm.v1.aes-sha2" sender_key="curve25519:NV/9yneJS3T/lH0TZdVLEDk4Ld3veH+nQG5cy2/KmXU" session_id="Cr7zjpSFe5n+MG4k8/yoVPKEBGXlkMFf0uJvwV+B3EM"

This seems to be because Alice did not see Bob's device when she hit /keys/query prior to sending her message:

[@user-1-alice:hs1] console.log   TRACE matrix_sdk_crypto::store::caches: Flagging user for key query, user: "@user-2-bob:hs1", sequence_number: 1
...
[@user-1-alice:hs1] console.log   DEBUG matrix_sdk_crypto::identities::manager: Created a /keys/query request, request_id: "8503e92bb9414f0ebd8cfbc3e7384fb4", users: ["@user-1-alice:hs1", "@user-2-bob:hs1"]
...
[@user-1-alice:hs1] console.log   DEBUG matrix_sdk_crypto::identities::manager: Handling a keys query response, request_id: "8503e92bb9414f0ebd8cfbc3e7384fb4", users: {"@user-1-alice:hs1", "@user-2-bob:hs1"}, failures: {}
...
[@user-1-alice:hs1] console.log   DEBUG matrix_sdk_crypto::identities::manager: Finished handling of the keys/query response, request_id: "8503e92bb9414f0ebd8cfbc3e7384fb4", new_devices: {}, changed_devices: {"@user-1-alice:hs1": {"LQSTRGAHYZ"}}, deleted_devices: {}, new_identities: {}, changed_identities: {}

I'm not sure why this happens though. Using:

• JS SDK: 29.1.0
• Synapse: v1.95.0

One interesting point with the test is whilst both Alice and Bob are registered prior to the test proper, Bob does not have OTKs at the time alice starts to sync, because bob := MustLoginClient is called after alice.StartSyncing(t). I wonder if this is affecting the /keys/query response somehow (which may imply it's a Synapse issue?).

Outcome

What did you expect?

The message was decrypted.

What happened instead?

The message was not decrypted.

Operating system

macOS

Browser information

Chrome

URL for webapp

N/A

Application version

JS SDK: 29.1.0

Homeserver

Synapse v1.95.0

Will you send logs?

Full logs attached.
js-js-happy-case-fail.log

[richvdh]

I think this is expected behaviour. It happens because Bob doesn't upload OTKs / device keys by the time Alice hits /keys/query -- so effectively Bob's device doesn't exist at the time Alice sends the message.

It crosses over somewhat with more general "device lists may not be up-to-date" (element-hq/element-meta#2411).